now i got new error, undefined reference to vtable for myWidget

Qt Code: 
  1. #include<QApplication>
  2. #include<QLabel>
  3. #include<QLineEdit>
  4. #include<QString>
  5.  
  6. class myWidget:public QWidget{
  7.     Q_OBJECT
  8.  
  9.     public:
  10.         myWidget(QWidget *parent=0);
  11.     private slots:
  12.         void processInput();
  13.     private:
  14.         QLabel *display;
  15.         QLineEdit *lineEdit;
  16. };
  17.  
  18. myWidget::myWidget(QWidget *parent)
  19.     :QWidget(parent)
  20. {
  21.     display=new QLabel;
  22.     lineEdit=new QLineEdit;
  23.  
  24.     connect(lineEdit, SIGNAL(returnPressed()), this, SLOT(processInput()));
  25.  
  26. }
  27.  
  28. void myWidget::processInput(){
  29.     QString text=lineEdit->text();
  30.     display->setText(text);
  31. }
  32.  
  33. int main(int argc, char **argv){
  34.     QApplication app(argc, argv);
  35.     myWidget window;
  36.  
  37.     window.show();
  38.     return app.exec();
  39. }
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